The present invention relates to a new continuous process for the production of mono- and polyisocyanates by the phosgenation of the corresponding mono- or polyamines wherein the reaction is carried out in special columns equipped with perforated plates.
The production of organic isocyanates by phosgenating the amines from which they are derived has hitherto been carried out in mixing tanks (e.g., DE-OS No. 1,468,445), cascades of mixing tanks (e.g., DE-PS No. 884,896), reaction columns filled with packing material (e.g., DE-OS No. 2,112,181) or empty columns (e.g. Ullmanns Encyclopadie der technischen Chemie, 4th Edition (1977), pages 351 et seq, in particular FIG. 2 on page 352). These methods frequently require integration of the apparatus in a circulating system for continuous operation (for example, in the process according to DE-OS No. 2,112,181) because a single passage through the reaction vessel is not sufficient for complete conversion.
It has now been found that a very significant improvement in the phosgenation reaction can be achieved by using special columns equipped with perforated plates through which the reaction mixture flows upwards from below. The process according to the invention described below is distinguished in particular by the following advantages:
In contrast to the columns with packing materials previously used, this reaction vessel does not clog. PA1 Substantially higher volume/time yields can be obtained even at lower reaction temperatures than in the known processes using empty columns, thereby saving energy. PA1 The yield of product is increased despite the comparatively low reaction temperatures and short residence times. PA1 Circulation is unnecessary, thereby allowing use of simpler apparatus.